The present invention relates to welding apparatus and systems, particularly Metal Inert Gas ("MIG") arc welding systems. The invention relates particularly to arc welding systems of the type utilized in mechanized and robotic welding.
Typically, a MIG welding system includes a welding gun or torch assembly which feeds a consumable wire electrode through a current pick-up tip which applies welding potential to the electrode. Such welding gun assemblies may, for example, be of the types disclosed in my U.S. Pat. Nos. 3,496,328 and 3,775,584. The gun assembly includes a main body or housing to which is removably mounted a welding nozzle which surrounds the welding tip and channels an inert shielding gas to the welding arc. The nozzle may be air or water cooled. The welding gun assembly must be serviced with the utilities which it requires for operation, such as water for nozzle cooling, gas for shielding the welding arc and electricity to effect the welding, as well as being provided with the consumable wire electrode. All of these utilities are fed to the welding gun assembly from associated supplies via utilities delivery means, which may include a portable utilities station of the type disclosed in my U.S. Pat. No. 4,210,796.
When the welding system is to be utilized in mechanized or automated applications, the welding gun assembly is fixedly mounted on the automated welding control equipment. For example, the welding gun assembly may be mounted on a permanent fixed mount to which workpieces are delivered for welding or, alternatively, might be mounted on a movable mount such as that of a robotic welding machine, which moves to the workpiece under remote control, and which may be pre-programmed.
In such prior welding systems, the replacement of the welding gun assembly or parts thereof is extremely inconvenient, particularly in the automated or robotic applications. Thus, for example, in the event of system malfunction or damage to the welding gun assembly, it is necessary to replace the complete assembly, including all the utilities delivery means all the way back to the wire drive system. This is a very costly procedure, not only because it is time consuming, but also because it may, particularly in factory applications, require the involvement of several different tradesmen, such as electricians, plumbers, welders and the like.
Furthermore, in robotic welding applications, the replaced welding gun assembly will not be in precisely the same location and orientation with respect to the robot unit as was the original gun assembly. Since this precise positioning is critical to maintenance of a pre-programmed welding path, the system must be recalibrated at the cost of additional time and labor.
The aforementioned U.S. application Ser. No. 648,967 discloses a docking assembly for a welding system, which permits the welding gun or torch assembly to be easily manually replaced at the welding station, without affecting the utilities delivery means upstream of the welding station, and without losing the precise positioning of the gun assembly in the system.
However, there are many occasions when only the nozzle assembly needs to be replaced, and not the entire gun assembly. For example, in normal operation the nozzle assembly may become clogged or fouled with spattering from the welding operation, thereby impeding the flow of shielding gas through the nozzle assembly to the welding arc. In such instances, it is necessary to shut down the welding operation to either clean the nozzle assembly in place, or replace it with a new nozzle assembly. While the nozzle assemblies of prior art welding guns, including the nozzle assemblies disclosed in the aforementioned copending application Ser. No. 648,967, can be removed, this cannot be done easily, particulary in the case of water-cooled nozzles. Thus, water cooled nozzles are provided with water conduits which are coupled to the rest of the gun assembly by threaded fittings which must be disconnected with the use of a wrench or other suitable tool. Furthermore, the supply of cooling water must be shut down at the source during such nozzle replacement to avoid extensive water spillage at the welding station. Such spillage can be extremely troublesome, particularly in the case of aluminum welding, since water is a source of hydrogen which seriously impairs the formation of porosity-free weldments in aluminum.